The invention relates to the devices for microbiological examination of a sample of liquid under pressure.
Such a device is already known through French patent 2 677 664, having an intake body, a filtering membrane and a drainage body. The intake body has a reservoir, in one wall of which a liquid input aperture is made, the membrane closing this reservoir by being welded on to the edge of the lateral wall of this reservoir, the drainage body being designed to support the membrane on the opposite side from the reservoir and being provided with a liquid output aperture, the intake body and the drainage body locking with one another by screwing by virtue of integrally moulded thread elements.
The taking of a sample to be examined is performed by connecting the input aperture of the reservoir of the intake body to a source of liquid under pressure, so that the reservoir fills with this liquid, which can leave therefrom only through the filtering membrane, this liquid being recovered from the other side of the membrane by the drainage body and emptied therefrom through the output aperture.
In order to avoid the liquid which has passed through the membrane escaping from the drainage body somewhere other than through the output aperture, the intake body has, around the membrane, a flange provided with a lip coming to rest on the drainage body in order to obtain the required sealing.
This makes it possibly notably, for example by collecting the liquid emptied through the output aperture in a graduated container, to know accurately the volume of the sample of liquid which has passed through the membrane.
EP 059 809 A discloses a disposable filtration unit for similar purposes but where the sample of liquid is not under pressure. This device comprises as intake body an open ended shell, and, as drainage body, a cup-shaped receptacle, a funnel-shaped support plate for the filtering membrane and a support pad laid on the support plate which is carried by an internal shoulder of the receptacle to which it can be permanently attached by a suitable cement or by ultrasonic welding. The lower end of the shell has a necked portion so that it can be received into a rim of the receptacle, the axial length of the necked portion and its position within the rim being such that there is some axial distance between the top of the receptacle rim and an edge of the necked portion. A plurality of vertical ribs are formed integral with the shell. These ribs have sufficient length to bridge this axial distance and can be attached to the upper end of the receptacle rim by ultrasonic welding so as to fix the shell to the receptacle. Because the attachment of the ribs to the receptacle occurs only at spaced intervals about the periphery of the receptacle, the ribs provides weak xe2x80x9cbreakawayxe2x80x9d points so as to facilitate removal of the shell from the receptacle. In one embodiment, a flat, annular gasket is disposed between the lower end face of the shell and the support plate, the inner periphery of this gasket being squeezed between an inner foot of the shell and the filtering membrane whereas the outer periphery of the gasket is squeezed by an outer foot of the shell and rests on the rim of the support plate, this gasket thus providing, on the one hand, a liquid-tight seal between the shell and the filtering membrane and, on the other hand, an air-tight seal between the shell and the support plate. In other embodiments, the support plate comprises an upstanding tongue which is received between the inner foot and the outer foot of the shell whereas the flat, annular gasket is replaced by a gasket which has been put in a space between the rim and the tongue of the receptacle.
U.S. Pat. No. 4,678,576 A discloses a device for similar purposes, but not for a liquid under pressure. The disclosed device comprises, as intake body, an open ended upper body, and, as a drainage body, a cup-shaped receptacle and a support plate, a locking rim being further provided to lock the intake body and the drainage body. The support plate is sandwiched between an upper collar portion of a collar included in the receptacle and an internal shoulder of a necked portion including the upper body, the ring being engaged respectively, by its internal thread, with the external thread of the lower portion of the collar of the receptacle and, by an upper rim, with the lower external shoulder of a split flange included in the upper body. In one embodiment, two O-rings are provided respectively on one side and on the other of the support plate whereas in another embodiment, a single H-shaped gasket is provided
The invention relates to a device of the same kind as known through French patent 2 677 664, but simpler, more convenient and more economical, both in manufacture and in use.
To that end it proposes a device for microbiological examination of a sample of liquid under pressure, having an intake body, a filtering membrane and a drainage body, said intake body having a reservoir, in one wall of which a liquid input aperture is made, said membrane closing said reservoir, said drainage body having means of supporting said membrane on the opposite side from said reservoir and a liquid output aperture, said intake body and said drainage body having integrally moulded mutual locking means; characterised in that said membrane is gripped annularly at the periphery between a first member forming part of said intake body and a second member forming part of said drainage body with one out of said first member and said second member having an elastomer seal by means of which it comes into contact with said membrane, and in that said locking means are adapted to allow the opening of said device by requiring only a separation movement between said first member and said second member, said locking means having means of axial latching between the intake body and the drainage body, one out of the latter having at least one axially oriented latching tab while the other has means of receiving said latching tab, which extends projecting from the edge of a skirt forming part of that one out of said intake body and said drainage body which includes it.
Thus, unlike the aforementioned earlier device known through French patent 2 677 664, where the locking means are constituted by thread elements, the opening of the device according to the invention is performed with no rotational movement between the intake body and the drainage body.
The device according to the invention therefore makes it possible to eliminate any risk of creasing the membrane at the time of opening the device where it is then in the wet state.
Furthermore, the elastomer seal, although it is present only on one of the faces of the membrane, makes it possible to obtain sealing on both faces of the membrane, that is to say both with the first member and with the second member, from the simple fact that said members grip the membrane, that is to say they are held close to one another, so that it is not necessary, in order to close the device according to the invention, to perform a rotational movement, unlike the above-mentioned earlier device known through French patent 2 677 664 which requires, so that the sealing lip on the intake body is applied with the required intensity on the drainage body, that assembly is carried out by screwing with a considerable torque.
The device according to the invention is therefore much simpler and more convenient to use than the above-mentioned earlier device known through French patent 2 677 664, and is furthermore simpler to manufacture, since there is no need, on the one hand, to make provision for achieving sealing between the membrane and the intake body by welding, and, on the other hand, sealing around the membrane between the intake body and the drainage body, given that, in the device according to the invention, the gripping of the membrane between the first member and the second member makes it possible to obtain these two instances of sealing directly.
Thanks to the fact that the locking means have means of axial latching between the intake body and the drainage body, the assembly of the device according to the invention is particularly simple, since it is sufficient to bring the intake body and the drainage body together in order to lock them by latching.
It should be noted that the elastomer seal, on account of its elasticity, takes up the play necessary for enabling latching, so that, once assembled, the intake body and the drainage body are held with no axial play with respect to one another.
The fact that one out of the intake body and the drainage body has at least one axially oriented latching tab while the other has means of receiving said latching tab, is preferred for reasons of simplicity and convenience, both in manufacture and in use.
Preferably, the membrane is held exclusively on account of it being gripped annularly at the periphery between said first member and said second member.
The manufacture and use of the device according to the invention are thus particularly simple, since no operation such as the sealing of the membrane existing in the earlier device has to be implemented, while, after opening of the device according to the invention, the membrane, which is fixed neither to the first member nor to the second member, can be recovered directly, for example with sterile tweezers in order to be put into culture in a conventional Petri dish.
Preferably again, said latching tab is connected to the remainder of that one out of said intake body and said drainage body which includes it, by a breakable zone.
The release of the locking means between the latching body and the drainage body can thus be performed by simple breaking of the latching tab, or even of a number of latching tabs if the device according to the invention has more than one.
According to other preferred characteristics, said drainage body has a circular table provided at its centre with means of supporting said membrane and having, around said support means, a wall having a surface situated facing said elastomer seal, which forms part of said intake body, said membrane being squeezed between said surface and said seal.
This arrangement offers in effect the advantage of being relatively simple to implement and of obtaining excellent results as regards sealing.
According to other preferred characteristics, for the same reasons, said output aperture of the drainage body is in the continuation of the internal passage of an output pipe disposed coaxially.
Preferably, said drainage body has, around said output pipe, an annular rib tapering towards its end.
This rib makes it possible in particular to drain the device according to the invention by placing it directly on a vacuum flask with said output pipe engaged in the central hole of the stopper of said flask and said annular rib resting on this stopper.
The invention also relates, in a second aspect, to a method for thus draining the device according to the invention.